In contrast to the high enantioselectivities observed in certain catalytic olefin (C.dbd.C bond) and ketone (C.dbd.O bond) hydrogenations, little success has been achieved in the catalytic asymmetric hydrogenation of the C.dbd.N bond. The limited success that has been reported is mostly involved with the reduction of imines.
H. E. Baumgarten et al., J. Org. Chem., 41(24), 3806 (1976), disclose the catalytic hydrogenation of N-1-phenylethyl-N'-carbo-tert-butoxyhydrazone to N-1-phenylethyl-N'-carbo-tert-butoxyhydrazine. It is stated that this is a general procedure but that it cannot be used for optically active hydrazines because the reductions are not stereoselective.
K. Harada, Asymmetric Synthesis, Volume 5, Academic Press, 1985, p. 360 describes the hydrogenation of optically active hydrazones to optically active amines. There is no disclosure nor suggestion of a method to generate optically active products from non-optically active starting materials.
J. Souppe et al., J. Organometallic Chemistry, 250, 237-236 (1983) report the reductive cleavage of the N--N bond in 1,2-diphenyl hydrazine by samarium diiodide to yield aniline in 55% yield after a 4 day reaction period. There is no disclosure concerning the reactivity of samarium diiodide with N-acylhydrazines.
The present invention provides processes for the asymmetric hydrogenation of N-acylhydrazones to optically active N-acylhydrazines, and the reductive amination of keto group-bearing compounds to corresponding chiral amino group-bearing compounds. The use of transition metal catalysts bearing chiral ligands in these processes provides products in optically active form. The present invention also provides a process for the reductive N--N bond cleavage of N-acylhydrazines.